Effects of Substrate Rheological Properties on Microbial Community and Biogas Production in Anaerobic Digestion

Abstract

The relationship between microbial communities and sludge rheological properties variation were studied using thermal hydrolysis sludge as a substrate. A set of mesophilic batch anaerobic digesters fed by rheologically different substrates of the same chemistry and organic matter content were set up. The interaction link between sludge rheology, physicochemical parameters, biogas production, and microbial characteristics was studied. The results proved that the suitable viscosity (0.036 Pa·s) promoted the degradation efficiency of organic matter (OM) in SM-2, which contributed to the highest OM degradation level, and the biogas yield was 7.59% higher than that of the control group. The dramatic drop in yield stress (τ0) and consistency coefficient (k) in reacter SM-2 also meant there was more fluid-like behavior of sludge and better mass transfer between OM and microorganisms after AD. The results of high-throughput 16S rDNA sequencing revealed that the proportion of the dominant archaea genus Methanothrix increased first and then decreased with increasing viscosity and had the highest relative abundance in SM-2. Bacteria phylum Firmicutes and Gram-negative Bacteroidetes dominated in all five reactors. The microbial metabolic functions predicted by FAPROTAX showed that sludge with higher viscosity had greater impact on hydrogenotrophic metabolism archaea. Substrate viscosity was significantly correlated with the richness and diversity of archaea community. These results revealed the effects of rheological properties on anaerobic digestion (AD) performance parameters and the microbial community behavior, indicating that the rheological properties could be a useful tool to monitor the operation of the digester.